After computer programming, the fuel supply program of the original car will be discarded, but a higher-level computer can retain all the sensor functions of the original car, which means that various fuel supply compensation programs can operate normally, and can also be changed. Smooth operation and practicality are not sacrificed for high performance. The biggest difficulty in refitting a programmable ECU is not the installation, but the setting and optimization of the fuel supply program. This often requires the use of experience and instruments, and can only be achieved through continuous testing. The current practice of the refitting factory is to first select a basic model as the basis, and then gradually correct it through actual operation and testing until it is satisfied. Several common problems in the process of refitting the ECU may be due to the fact that the functions and working principles of the ECU are “invisible” different from other mechanical systems. In addition, most auto repair shops and even 4S shops do not understand it, and cannot repair or repair it. Solve the problems generated by ECU, thus forming the mystery of ECU.